251
Polonium [Po, 84]
Results showed that the activity concentrations of naturally occurring radionuclides,
especially those of 210 Po and 40 K, were much higher than those of anthropogenic radionuclides. Calculations of effective dose, due to ingestion of a given radionuclide in the
food, depend on the concentration of the radionuclide, the amount of food eaten, and
the dose coefficient, or the effective dose per unit intake of the radionuclide. The dose
coefficient is essentially dependent on the body uptake and the distribution and retention
by body organs (Hunt and Rumney 2007).
210 Polonium is a high-energy α-emitter (radioactive half-life of 138 days) that
presents a radiation hazard only if taken into the body, for example, by ingestion,
because of the low range of α-particles in biological tissues. As a result, external
contamination does not cause radiation sickness. Ingested 210 Po is concentrated initially in red blood cells, and then the liver, kidneys, spleen, bone marrow, gastrointestinal tract, and gonads. 210 Po is excreted in urine, bile, sweat, and (possibly)
breath, and is also deposited in the hair. After ingestion, unabsorbed 210 Po is present
in the feces. The elimination half-life time in humans is approximately 30–50 days.
In the absence of medical treatment, the fatal oral amount is probably in the order of
10–30 μg. Ingested 210 Po can cause after radiation sickness symptoms (ARS). This
is characterized by a prodromal phase, in which nausea, vomiting, anorexia, lymphopenia, and sometimes diarrhea develop after exposure. Higher radiation doses
cause a more rapid onset of symptoms and a more rapid reduction in lymphocytes.
The triad of early emesis followed by hair loss and bone marrow failure is typical of
ARS (Jefferson et al. 2009).
210 Po and 210 Pb are the most important representatives of the natural marine radioactivity, and they can be considered the major contributors to radiation doses received
by humans, among natural radionuclides in the marine environment (Table 34.1).
TABLE 34.1
210 Po Activity Concentration in Fish from
Different Areas in the World (Bq/kg FW)
Country
Concentration
Lebanon
0.22–47.82
Syria
0.27–27.48
Japan
0.6–26.0
Denmark
0.35–0.9
Portugal
0.2–11
Australia
0.09–44.1
South Africa
2.2–20.3
Brazil
0.5–5.3
America
0.4–153.3
Poland
0.9–5
Source: El Samad, O. et al., Leban. Sci. J., 11, 39–45, 2010.
FW, fresh weight.